Pump stand with improved pump control

ABSTRACT

Integrated, stand-alone, multiple-purpose pump stands are provided for controlled pumping of different liquids from a stand-mounted tank to a downstream use location, e.g., a seed treating device. The pump stands are equipped with an operating assembly including a liquid tank, a powered pump, a liquid flow line equipped with a flow meter from the tank and pump to the use location, and a programmable digital control device. During operation, the control device serves to approach and maintain the flow rate from the pump stand at or about a desired setpoint flow rate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is broadly concerned with improved, stand-alonepump stands for controlling the flow rate of a liquid from a liquidsource. More particularly, the invention is concerned with such pumpstands, and corresponding methods, wherein the flow rate of liquid israpidly approached and maintained at or about a preselected setpointflow rate.

2. Description of the Prior Art

In many agricultural applications, seeds are coated with various liquidchemicals prior to planting. Such liquids may include pesticides, growthstimulants, or plant nutrients, and these liquids have a variety ofdifferent physical characteristics such as viscosities and drying rates.Seed treaters have been developed for coating large volumes of seed onan industrial basis. Generally, such treaters include a seed inlet, asprayer or other device for applying coating liquids to the surfaces ofthe seeds, and some sort of rotating drum or the like to assure uniformseed coating. As such, it is necessary to deliver the treating liquidsto the application device at a uniform flow rate. That is to say, if theliquids are delivered at variable flow rates, then the seeds will bedifferentially coated, depending upon the instant at which the seedswere treated with the liquid.

There are two basic types of pumping systems for handling and pumping ofseed treating liquids delivered to downstream seed treaters. Most often,these systems are mounted on a stand or other support structure separatefrom the seed treaters. These systems include mix tank(s), pump(s),tubing system(s), and various types of monitoring and control equipment.

The first type is a “manual” system that uses a controller of some typeto drive the pump motor(s) based upon a proportional signal. Forexample, the pump motor(s) can be operated at 50% of the maximum speedsthereof. If the operator needs to adjust the liquid flow rate exitingthe pump, the flow rate must be manually adjusted using the controller.In these types of systems, the flow rate is typically determined eitherby an in-line flow meter, or a “catch and time” technique wherein thevolume of liquid delivered over a selected period of time is measured,and the flow rate is thus determined. Some of these manual systems alsohave the ability to read a signal from a downstream seed treater toeither turn on the pump(s), or to terminate the operation thereof.However, none have the ability to automatically adjust liquid flow rateover time. Furthermore, these systems do not have any means ofautomatically reporting the volume of liquids pumped, so the operatormust either use a flow meter totalizer or some sort of mass balancing tocalculate the total chemical usage for a given time period.

The second type of system is an automated or automatic system, and isgenerally plug-connected to a PLC-based controller that performs all ofthe logical steps for pumping operations. In these systems, an operatormay set a desired flow rate, and the pump speed will automaticallyadjust to meet that desired flow rate, based upon information receivedby the PLC from a connected flow meter. This is generally done via a PI(proportion-integral) or PID (proportion-integral-derivative) softwarecontrol loop. These systems also have automatic reporting capabilitiesthat show total chemical usage.

In many instances, upgrades are available for the manual and automaticsystems, which allow adjustment of the liquid flow rate duringoperation. These upgrades allow an operator to offset via a multiplierany consistent inaccuracies that the flow meter may display. Suchinaccuracies occur quite often with the use of standardvolumetric/electromagnetic flow meters normally employed. All of theknown manual system upgrades provide only a display device, and do notprovide any control function. Moreover, they have only one adjustableoffset or multiplier per flow meter.

As such, there are presently no “stand-alone” liquid pump stands whichallow the operator to choose a desired setpoint flow rate, with theon-board controllers serving to automatically maintain the set pointflow rate via adjustment of pump speeds. Moreover, none of the known“automatic” pump stands makes use of multiple PI or PID control loops toaccomplish fast pump speed changes and steady pump speed control.Additionally, all adjustable flow rate displays for “stand-alone” pumpstands have only one available adjustment for each flow meter. Thismeans that if an operator wishes to run a different liquid through thesame flow meter, then the operator must recalibrate the display of theflow meter, without the capacity to retain previously used calibrationsettings.

SUMMARY OF THE INVENTION

The present invention overcomes the problems outlined above and providesa movable stand-alone pump stand, which can be used to good effect withseed treater(s) so as to properly coat agricultural seeds with specifiedand essentially identical amounts of liquid chemicals. The pump standsof the invention generally include a supporting frame assembly(preferably of generally L-shaped design), which supports a completeoperating assembly. That is to say, the operating assembly includes aliquid chemical tank, a powered pump, a flow line coupled with the tankand pump for delivery of liquid from the tank to a downstream seedtreater, a flow meter operably attached to the flow line to determinethe flow rate of liquid through the flow line during operation, and aprogrammable digital device operably coupled with the pump and flowmeter in order to deliver liquid from the flow line at or about apreselected setpoint flow rate. The modular, stand-alone design of thepump stands greatly facilitates seed coating operations, and allows anoperator to easily control all steps associated with such coatingpractices.

The digital device controller can be used to control the various pumpstand operations described previously. However, from an operationalstandpoint, the ability to quickly approach and maintain a setpoint flowrate of liquids is of prime importance. As used herein, “at or about asetpoint flow rate” refers to the ability of the pump stands of theinvention to maintain a preselected setpoint flow rate over time, with arelatively small plus or minus variance from the exact set point flowrate, e.g., plus or minus about 1-10%. It will be appreciated that the“plus or minus” variance is largely determined by the program variablesdescribed herein.

Thus, the invention further includes a method for controlling the flowrate of a liquid from a liquid source, which is applicable to fluids ingeneral, but which is especially designed for seed-coating operations.The method broadly comprises the steps of:

(a) establishing a desired setpoint flow rate for the liquid from thesource;

(b) pumping the liquid from the source using a powered pump, anddetermining the flow rate of the pumped liquid from the pump;

(c) controlling the operation of the powered pump to pump the liquid ata flow rate at or about the setpoint flow rate, by periodicallycomparing the determined flow rate of the liquid from the source withthe setpoint flow rate, and:

-   -   (i) if the difference between the determined flow rate and the        setpoint flow rate is at or above a first predetermined        magnitude, operating the pump so as to alter the operation of        the pump at a relatively high aggressive first correction rate,        so that the determined flow rate approaches the setpoint flow        rate at the aggressive first correction rate;    -   (ii) if the difference between the determined flow rate and the        setpoint flow rate is at or above a second predetermined        magnitude but below the first predetermined magnitude, operating        the pump so as to alter the operation of the pump at a        relatively low moderate second correction rate lower than the        first correction rate, so that the determined flow rate        approaches the setpoint flow rate at the moderate second        correction rate; and    -   (iii) continuing the controlling steps (c)(i) and (c)(ii)        throughout the flow of liquid from the liquid source.

In preferred forms, the method includes a further step if the differencebetween the determined flow rate and the setpoint flow rate is at orabove a third predetermined magnitude but below the second predeterminedmagnitude, operating the pump so as to alter the operation of the pumpat a relatively lower conservative third correction rate lower than thesecond correction rate, so that the determined flow rate approaches thesetpoint flow rate at the conservative third correction rate.

As noted previously, these method steps are carried out using aprogrammable digital device. The digital device may be user-operatedwhere an operator inputs the setpoint flow rate and mode of operation,or such information may be electronically communicated to the digitaldevice. During operation, the flow meter may be calibrated to ensurethat the determined flow rate reported by the meter is the actual flowrate of the liquid. Such calibration may be carried out by measuring theflow of liquid through the flow meter for a selected period of time togive an actual flow rate for the liquid, comparing the measured flowrate with the flow rate reported by the flow meter, determining acorrection factor unique to the flow meter and liquid, and storing thecorrection factor in electronic memory. A useful feature of the presentinvention is that the pump stand is equipped with electronic memory sothat a plurality of correction factors may be stored for a correspondingplurality of different liquids. Hence, once the flow meter is calibratedand stored for a particular liquid, that calibration information can beretrieved when the corresponding liquid is again used with the pumpstand.

In order to rapidly approach and maintain the flow rate of liquid fromthe pump stand at or about the setpoint flow rate, the digital controldevice is preferably programmed to apply a feedback control loopaccording to a tiered control scheme in order to carry out the steps(c)(i) through (c)(iii) described above. To this end, a multi-tieredproportional-integral-derivative (PID) control loop, or a multi-tieredproportional-integral (PI) control loop, is employed carry out thesesteps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective view of a pump stand in accordance withthe invention;

FIG. 2 is a rear perspective view of the pump stand depicted in FIG. 1;and

FIG. 3 is a schematic flow diagram illustrating the preferred digitalprocessor control of the pump stand.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Pump Stand

Turning now to FIGS. 1-2, a pump stand 10 is illustrated. The stand 10broadly includes a supporting frame assembly 12, a tank assembly 14, afirst valve and conduit assembly 16, a pump and conduit assembly 18, asecond valve and conduit assembly 20 with an in-line flow meter 22, acalibration tube 24, and control assembly 26. The pump stand 10 isdesigned to hold liquid chemical(s), typically used for seed coating,and to deliver calibrated amounts of the chemical(s) to a seed treateror the like. The pump stand 10 is completely self-contained, and has anumber of features greatly facilitating accurate dispensing ofchemical(s).

In more detail, the frame assembly 12 includes a box-like, quadrate base28 presenting an uppermost mounting plate 30 and having a pair ofupstanding, opposed frame arms 32 and 34 secured to the rear end of base28. An equipment mount plate 36 extends between the arms 32, 34, and anuppermost rigidifying cross-brace 38 interconnects the arms 32, 34 attheir uppermost ends. A generally U-shaped bumper 40 is secured to thearms 32, 34 and extends rearwardly therefrom.

The tank assembly 14 includes a triangular tank base 42 comprising threeupstanding legs 44 secured to the mounting plate 30 with a generallytriangular, intermediate apertured support plate 46 secured to the legs44 above mounting plate 30. The upper end of the base 42 includes thegenerally circular hoop 48 likewise supported by the legs 44 adjacentthe upper ends thereof. The base 42 is designed to support aconical-bottom liquid tank 50 including a generally circular upper wall52 and a substantially frustoconical lower wall 54 having a lowermostliquid outlet 56. An upper tank cover 58 is positioned atop the circularwall 52 in order to close the tank 50 and to allow filling thereofthrough the ports 60. The cover 58 also supports an agitator drive motor62 with an associated gear box 64. A central agitator shaft (not shown)is operably coupled with gear box 64 and extends into the confines oftank 50. The agitator shaft has conventional mixing elements so that thechemical(s) within tank 50 may be agitated to ensure proper mixingthereof.

The first valve and conduit assembly 16 includes a delivery pipe 66operably coupled with tank outlet 56 and equipped with a diverter valve68. The output end of pipe 66 is equipped with a tee 70. A drain conduit72 is secured to one end of the tee 70, whereas a liquid deliveryconduit 74 is secured to the opposite end of tee 70. The drain conduit72 is also equipped with a two-way diverter valve 76. The assembly 16also includes a two-way diverter valve 78 supported on a forwardlyextending plate 80. The delivery conduit 74 is secured to the input ofvalve 78. A pair of output conduits 82 and 84 are also coupled withvalve 78. Output conduit 82 extends to and is coupled with calibrationtube 24, whereas output conduit 84 extends to and is connected with aliquid filter 86 secured to the rear face of mounting plate 36.

The pump and conduit assembly 18 includes a lower manifold block 88secured to the rear face of equipment mounting plate 36, an intermediatepumping assembly 90, and an upper manifold block 92. The filter 86 iscoupled to lower manifold block 88 for delivery of filtered chemicals toa pair of outputs 96, each equipped with a short conduit 98. Theintermediate pumping assembly 90 includes an electrical drive motor 100and a pair of pumping heads 102 and 104. The output of the head 104 isdelivered through short conduits 106 to upper manifold block 92, whichdelivers the pumped liquid through output pipe 108 equipped with anupstanding turbulence-minimizing pipe 110.

The second valve and conduit assembly 20 includes a liquid conduit 112coupled with the end of pipe 108 and equipped with the in-line flowmeter 22, and a dual valve assembly 114 mounted on an upstanding plate116 and having upper and lower valves 118 and 120. The upper end ofconduit 112 is coupled with the lower valve 120, and the outputs thereofare respectively coupled with a coiled liquid delivery line 122, whichis coupled to a downstream seed treater or other device, and to theinput of upper valve 118. The outputs of valve 18 are respectivelycoupled with a recirculation conduit 124 leading to tank 50, and acalibration tube conduit 126.

The calibration tube is in the form of an elongated upright tube 127equipped with upper and lower end caps 128 and 130, and a volumetricscale (not shown) imprinted on the body of the tube 127. As illustrated,the conduit 126 is secured to the upper end cap 128, whereas outputconduit 82 is secured to lower end cap 130.

The control assembly 26 includes a conventional electrical junction box132 and a controller 134 equipped with a touch pad output 136. Thesequential operation of the pump stand 10 is governed and controlled bythe controller 134, and this operation will be described in detail inconnection with FIG. 3.

In alternative forms of the pump stand 10, a weigh scale (not shown) maybe used in lieu of mounting plate 30 in order to provide continuousmonitoring of the weight of chemical(s) within the tank.

Operation of the Pump Stand

There are four basic modes of operation for the pump stand 10, namelyinitial recirculation of liquid, pump calibration, normal calibrateddelivery of liquids to the downstream seed treater or other device, anda reverse or flush operation.

The recirculation mode would typically be used during startup of thepump stand in order to ensure that the liquid chemicals within the tank50 are uniformly mixed. In order to recirculate, the agitation drivemotor is operated to mix the chemicals within tank 50. Also, the valve68 is open to prevent delivery of liquid through outlet 56 and pipe 66,the valve 76 is closed, and the valve 78 is opened to deliver liquidthrough filter 86, lower manifold block 88, and pumping heads 102, 104.The lower valve 120 is set to deliver the pumped liquid to upper valve188, which is set to deliver through recirculation conduit 124, back totank 50. It will thus be seen that operation of the pump assembly 90draws liquid front the tank 50 and ultimately recirculates this fluidback to the tank.

After adequate circulation is achieved, the stand 10 may be used ifneeded to calibrate the flow rate of the pumping assembly 90 in order todeliver consistent volumes of liquid per unit time through the deliveryline 122. Specifically, in this mode of operation, the upper valve 118is positioned so as to deliver liquid through the calibration tubeconduit 126. This continues for a predetermined period of time (e.g.,one minute), and the amount of liquid collected with calibration tube 24is determined using the volumetric scale markings on tube 127. If thetarget output of the pumping assembly 90 is 50 ounces/minute, this canbe determined using the collected amount of liquid. If the flow rate iseither too high or too low relative to the desired output rate, thecontroller 134 can be operated to compensate for the difference. In thisoperation, the touch screen is tapped until a calibration screenappears, whereupon the underage or overage flow rate is adjusted to thetarget rate. The controller 134 thus provides a signal u(t) to thepumping assembly 90 to speed up or slow down, as the case may be, so asto deliver a consistent flow rate output to the downstream seed treateror the like. The controller 134 is also provided with continuous flowrate data owing to the presence of the in-line flow meter 22. Oncecalibration is achieved, the valve 78 is manipulated so that the pumpingassembly 90 removes the liquid from the calibration tube 24, which isdiverted through the pumping assembly 90, as described previously.

After optional calibration, the pump stand 10 is typically used in anormal delivery mode. This requires only that the valve 78 bemanipulated after emptying of the calibration tube 24 so that thepumping assembly 90 draws liquid from the tank 50, and manipulation oflower valve 120 so that the pumped liquid is directed to the deliveryline 122 for downstream use.

At the end of a given run, it may be necessary to change the liquidchemical(s) within tank 50 in order to deliver different chemical(s) fora subsequent run. In such a case, the valve 76 is opened to deliverliquid to the drain conduit 72, and the pump drive motor 100 isreversed. This serves to remove all liquids within the pump assembly andother conduits, while the material remaining in tank 50 is allowed toflow by gravitation through the conduit 72.

Before a fresh batch of liquid chemical(s) is delivered to tank 50, itmay be desirable to flush the entire system. Water or other cleaningfluids are directed to tank 50, whereupon the pump stand 10 is operatedin recirculation mode, as described above, followed by a second flushoperation. The tank 50 can then be refilled with the necessary liquidchemical(s) for the subsequent run.

Automated Control of Pump Stand

As mentioned above, the controller 134 governs operation of the pumpstand 10. The controller 134 is preferably a digital integrated circuitand may be a general use, commercial off-the-shelf computer processor, aprogrammable logic device configured for operation with the pump stand10, or an application specific integrated circuit (ASIC) especiallymanufactured for use with the pump stand 10. The controller 134 mayinclude two or more separate integrated circuits cooperating to controloperation of the pump stand 10, and may include one or more analogelements operating in concert with or in addition to the digital circuitor circuits. The controller 134 may include or communicate with a memoryelement configured to store data, instructions, or both for use by thecontroller 134. The controller 134 is also referred to herein aprogrammable logic controller or PLC.

An exemplary sequence of control steps performed by the controller 134is illustrated in the flow diagram of FIG. 3. Operation of thecontroller 134 may begin manually in response to a user input orautomatically in response to a start signal received from an externaldevice such as a seed treater. A user may manually launch a treatmentapplication process by engaging a button or other user interface elementdesignated for that purpose, as depicted in block 200, or may place thecontroller 134 in automatic start mode, as depicted in block 202. Whenthe controller 134 is in the automatic start mode it automaticallylaunches the process upon receiving the start signal, as indicated inblock 204.

Whether the controller 134 begins the process in response to a manualinput from a user or in response to a start signal, it first determinesa mode of operation, as depicted in block 206. The controller 134 maydetermine the mode of operation by, for example, prompting the user toselect the mode or by retrieving a previously-stored setting indicatingthe mode of operation. If a pump percentage mode is selected, asdepicted in block 208, the controller 134 prompts the user to enter adesired percentage, as depicted in block 210, corresponding to apercentage of the maximum output or speed of the motor. The controller134 then communicates the control signal u(t) to the pump motor to causethe pump motor to operate at the desired percentage, as depicted inblock 212, until the user stops the motor. The pump percentage mode maybe used, for example, during initial recirculation, while the targetrate mode may be used during pump calibration and normal calibrateddelivery.

If the controller 134 operates in the target rate mode 214 thecontroller 134 determines a flow rate setpoint, as depicted in block216. The flow rate setpoint is the desired or target application flowrate. The controller 134 may prompt the user to submit the setpoint, forexample, or may retrieve it from memory or receive it from an externaldevice. The flow rate setpoint may change during operation, as explainedbelow.

When the controller 134 has determined the flow rate setpoint, it thencontrols the pump motor to apply treatment as closely as possible to thesetpoint. More specifically, the controller 134 determines a flow rateerror e(t) corresponding to a difference between the actual flow rate(as indicated by the in-line flow meter 22) and the setpoint and uses afeedback control loop function to modify the actual flow rate tominimize the error. The value of e(t) may be expressed in various ways,including as a raw difference or as a percentage of the setpoint. Thecontroller 134 applies a feedback control loop to control the pump motoraccording to a tiered control scheme wherein a more aggressive (faster)response is applied to greater values of e(t) and a more conservative(slower and more stable) response is applied to smaller values of e(t).More particularly, the controller 134 uses a multi-tieredproportional-integral-derivative (“PID”) or proportional-integral (“PI”)control loop to manipulate process control inputs (e.g., a motor controlsignal) to minimize e(t). In some embodiments, the controller 134generates a pump motor control signal according to the following controlequation:

${u(t)} = {{K_{p}\left\lbrack {{e(t)} + {\frac{1}{T_{n}}{\int_{0}^{t}{{e(\tau)}\ {(\tau)}}}} + {T_{v}\frac{}{t}{e(t)}}} \right\rbrack} + U_{Offset}}$

wherein—

-   -   u(t) is the pump motor control signal;    -   e(t) is the error function defined above;    -   K_(P) is a proportional coefficient;    -   T_(n) is an integral coefficient;    -   T_(v) is a derivative coefficient; and    -   U_(Offset) is an offset variable for the motor control signal.

The controller 134 is configured to manipulate the values of K_(p),T_(n) and T_(v) to shift the PID control function between a moreaggressive response and a more conservative response. Generally,increasing the value of K_(p) increases the aggressiveness of thecontrol loop while increasing the value of T_(n) decreases theaggressiveness of the control loop. The values of K_(p) and T_(n) willdepend on other, implementation-specific variables such as the number ofpump heads associated with the pump motor. The value of U_(Offset) maybe specific to particular application chemicals and/or particularapplication processes.

In one preferred embodiment, the variable T_(v) is set to zero toentirely eliminate the derivative term from the equation such that thecontroller 134 implements a PI control function. Alternatively, thevalue of T_(v) may be set to a very low number to minimize the influenceof the derivative term on the output. By way of example, for aggressiveoperation, the value of K_(p) may be within the range of from about 0.8to about 0.5, for moderate operation may be within the range of fromabout 0.05 to about 0.2, and for conservative operation may be withinthe range of from about 0.02 to about 0.5. For aggressive operation, thevalue of T_(n) may be within the range of from about 1.0 to about 4.0,for moderate operation may be within the range of from about 2.0 toabout 5.0, and for conservative operation may be within the range offrom about 4.0 to about 6.0. Table 1 illustrates exemplary values ofK_(p) and T_(n) for aggressive, moderate and conservative loops when thepump motor is driving one pump head, two pump heads and three pumpheads.

TABLE 1 1 Pump Head 2 Pump Heads 3 Pump Heads Aggressive Loop K_(p) =0.2 K_(p) = 0.15 K_(p) = 0.1 T_(n) = 2.0 T_(n) = 2.5 T_(n) = 3.0Moderate Loop K_(p) = 0.1 K_(p) = 0.085 K_(p) = 0.075 T_(n) = 3.0 T_(n)= 3.5 T_(n) = 4.0 Conservative Loop K_(p) = 0.01 K_(p) = 0.01 K_(p) =0.01 T_(n) = 5.0 T_(n) = 5.0 T_(n) = 5.0

Returning again to FIG. 3, the controller 134 begins operation byentering the aggressive control loop and communicating the controlsignal u(t) to the pump motor, as depicted in block 218. The controller134 periodically compares the actual flow rate with the setpoint todetermine if e(t) has fallen below an aggressive threshold, as depictedin block 220. The aggressive threshold may be, for example, betweenabout 20% and about 40%, and may particularly be about 25%, about 30% orabout 35%. If the actual flow rate has fallen below the aggressivethreshold, the controller 134 shifts to the moderate control loop andcontinues communicating the control signal u(t) to the pump motor, asdepicted in block 222. The controller 134 periodically compares theactual flow rate with the setpoint to determine if e(t) has fallen belowa moderate threshold, as depicted in block 224. The moderate thresholdmay be, for example, between about 10% and about 20%, and mayparticularly be about 12%, about 15% or about 18%. If e(t) has fallenbelow the moderate threshold, the controller 134 shifts to theconservative control loop and continues communicating the control signalu(t) to the pump motor, as depicted in block 226. If e(t) has not fallenbelow the moderate threshold, the controller 134 returns to block 220 todetermine if e(t) is below the aggressive threshold.

When the controller 134 is operating in the conservative control loop,it remains in the conservative control loop until the user presses astop button, until the setpoint changes as depicted in block 228, oruntil e(t) exceeds the moderate threshold. If the setpoint changes thecontroller 134 shifts back into the aggressive control loop to bring theactual flow rate near the setpoint as quickly as possible, then shiftsback into the moderate and conservative control loops as e(t) decreases,as explained above.

The user may initiate the reverse or flush operation set forth above byengaging a button or other user interface element designated for thatpurpose, as depicted in block 230, wherein the controller 134 drives thepump motor in reverse, as depicted in block 232. The controller 134continues driving the pump motor in reverse until the user presses astop button.

The controller 134 may store operational parameters associated withparticular chemical mixtures and/or particular processes so that when auser reinitiates a process that was previously run the controller 134recalls the parameters associated with that process, thus relieving theuser of the burden of recalibrating the pump stand 10 each time aprocess is run. Using the touch pad 136, for example, the user maycalibrate the pump stand 10 for use with a first chemical mixture. Firstcalibration information specific to the first chemical mixture iscreated and used, for example, to adjust the output of the flow meter22. The controller 134 stores the first calibration information in thememory. When the pump stand 10 is subsequently used with a differentprocess that involves a second chemical mixture the user calibrates thepump stand 10 for the second mixture. The controller 134 associatessecond calibration information with the second mixture and stores thesecond calibration information in memory. This process may be repeatedfor multiple chemical mixtures, wherein the controller 134 storesseparate calibration information for each of the chemical mixtures.

Thereafter, each time the user desires to use the first chemical mixturehe or she simply selects the first mixture via the touch pad 136 whereinthe controller 134 retrieves the first calibration information frommemory. In this manner, the controller 134 may retrieve and useoperational parameters associated with any of the previously usedchemical mixtures. While the discussion above has focused on the use ofcalibration information used to adjust the output of the flow meter 22,the operational parameters stored in memory and retrieved by thecontroller 134 may also be associated with any of the variables K_(p),T_(n), T_(v), U_(Offset).

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.(canceled)
 7. (canceled)
 8. (canceled)
 9. (canceled)
 10. (canceled) 11.(canceled)
 12. An integrated pump stand operable to deliver liquid at acontrolled flow rate, comprising: a supporting frame assembly; anoperating assembly supported by the frame assembly and including— a tankoperable to hold a liquid to be delivered; a powered pump; a flow lineoperably coupled with said tank and pump for delivery of liquid from thetank; a flow meter operably attached to said flow line to determine theflow rate of liquid through said flow line; and a controller deviceoperably coupled with said pump and flow meter in order to deliverliquid from said flow line at or about a preselected setpoint flow rate.13. The pump stand of claim 12, said controller device being a digitaldevice programmed to continually monitor and adjust the flow rate ofsaid liquid by control of said pump, to maintain the liquid flow rate ator about said setpoint flow rate.
 14. The pump stand of claim 12, saidcontroller device being a digital device programmed to: (a) control theoperation of said powered pump so as to pump the liquid at a flow rateat or about said setpoint flow rate, by periodically comparing thedetermined flow rate of the liquid from said source with said setpointflow rate, and: (i) if the difference between the determined flow rateand the setpoint flow rate is at or above a first predeterminedmagnitude, operating said pump so as to alter the operation of the pumpat a relatively high aggressive first correction rate, so that thedetermined flow rate approaches said setpoint flow rate at theaggressive first correction rate; (ii) if the difference between thedetermined flow rate and the setpoint flow rate is at or above a secondpredetermined magnitude but below said first predetermined magnitude,operating said pump so as to alter the operation of the pump at arelatively low moderate second correction rate lower than said firstcorrection rate, so that the determined flow rate approaches saidsetpoint flow rate at the moderate second correction rate; and (iii)continuing said controlling step (a)(i) and (a)(ii) throughout the flowof liquid from said liquid source.
 15. The pump stand of claim 14, saiddigital device also programmed to control the operation of said poweredpump such that if the difference between the determined flow rate andthe setpoint flow rate is at or above a third predetermined magnitudebut below said second predetermined magnitude, and to operate said pumpso as to alter the operation of the pump at a relatively lowerconservative third correction rate lower than said second correctionrate, so that the determined flow rate approaches said setpoint flowrate at the conservative third correction rate.
 16. The pump stand ofclaim 12, including a human operator interface operably coupled withsaid controller device permitting entry of said setpoint flow rate. 17.The pump stand of claim 12, including calibration apparatus operable todetermine the actual flow rate of said liquid.
 18. (canceled)
 19. Thepump stand of claim 12, said controller device having memory operable tostore a plurality of flow rate correction factors for a correspondingplurality of different liquids.
 20. The pump stand of claim 12, saidcontroller device being programmable and operable to apply a feedbackcontrol loop according to a tiered control scheme.
 21. The pump stand ofclaim 20, said controller programmed to employ a multi-tieredproportional-integral-derivative (PID) control loop.
 22. (canceled) 23.The pump stand of claim 12, said tank operable to hold a seed coatingliquid.